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A 36 by 48 inch window needs a 46 inch rod, 69 inch panel width, and 60 inch floor-length panels. Enter your window size and length style to get all three numbers before you buy.
Curtains that are too short or too narrow are the most common window-dressing mistake, and both are easy to avoid: the rod extends past the window, the panels are wider than the rod so they gather, and the length matches how the panels should hang. Enter your window and pick a length style.
Three rules, stated plainly so every number is reproducible. First, the rod is mounted 4 inches above the window top, and it extends 5 inches past the window on each side, so rod length equals window width plus 10 inches. Second, panel width is 1.5 times the rod length for standard fullness: panels narrower than the rod cannot gather, and they look flat when closed. For a fuller, luxe look, use 2 times the rod length instead — the calculator uses 1.5 times, so double the panel width yourself if you want that look. Third, panel length is measured from the rod: sill length equals the window height, apron length is height plus 4 inches, and floor length is height plus 12 inches. Because the rod sits 4 inches above the window top, the floor rule assumes a standard sill-to-floor gap; for very tall windows or windows close to the floor, measure from your actual rod position to the floor instead of trusting the rule.
Every row below is computed by the same three rules: rod equals window width plus 10 inches, panel width equals 1.5 times the rod, and floor panel length equals window height plus 12 inches. Read across for your window size, or use the calculator above for a size not listed here.
| Window (W × H, in) | Rod length (in) | Panel width (in) | Floor panel length (in) |
|---|---|---|---|
| 24 × 36 | 34 | 51 | 48 |
| 30 × 36 | 40 | 60 | 48 |
| 36 × 48 | 46 | 69 | 60 |
| 48 × 48 | 58 | 87 | 60 |
| 60 × 48 | 70 | 105 | 60 |
| 72 × 48 | 82 | 123 | 60 |
| 36 × 60 | 46 | 69 | 72 |
| 48 × 60 | 58 | 87 | 72 |
| 60 × 60 | 70 | 105 | 72 |
| 72 × 60 | 82 | 123 | 72 |
| 96 × 60 | 106 | 159 | 72 |
| 120 × 72 | 130 | 195 | 84 |
| Output | Formula | What it means |
|---|---|---|
| Rod length | Window width + 10 in | 36 + 10 = 46 in at the defaults, 5 in per side. |
| Panel width | Rod length × 1.5 | 46 × 1.5 = 69 in at the defaults, standard fullness. |
| Sill length | Window height | 48 in for a 48 in window, measured from the rod. |
| Apron length | Window height + 4 in | 48 + 4 = 52 in for a 48 in window. |
| Floor length | Window height + 12 in | 48 + 12 = 60 in at the defaults, measured from the rod. |
These are standard sizing rules, not a substitute for measuring your own window and wall. Rod brackets, finials, and rings add length beyond the rod itself, and a wall with a corner, a radiator, or a door frame on one side may not allow 5 inches of extension on both sides. Panel widths are sold per panel, so divide the total panel width by the number of panels you plan to hang, and check each panel's stated width before buying. Hemming, puddling, and header styles change the finished length, so for floor-length panels in a room you care about, measure from the rod position you actually mount to the floor and compare with the calculator's rule.
Bright Side Kit. "Curtain Size Chart: Rod, Panel Width & Length Calculator." https://brightoolbox.com/curtain-size-chart/ Accessed October 24, 2026.Window width plus 10 inches: 5 inches past the window on each side. A 36 inch window needs a 46 inch rod, and a 60 inch window needs a 70 inch rod.
For standard fullness, total panel width should be 1.5 times the rod length: 69 inches of panel for a 46 inch rod. For a fuller, luxe look, use 2 times the rod length, or 92 inches for the same rod.
In this calculator, window height plus 12 inches, measured from the rod: 60 inches for a 48 inch window. Because the rod sits 4 inches above the window top, measure from your actual rod position to the floor for tall or low windows.
Sill length ends at the window sill and equals the window height; apron length hangs just below the sill at height plus 4 inches; floor length reaches the floor at height plus 12 inches, all measured from the rod.
This calculator assumes 4 inches above the window top, which is the standard rule used for its length figures. Mounting higher makes panels longer, so re-measure from the real rod position if you mount higher.
Yes: the calculator's panel width is the total across all panels. For two panels on a 46 inch rod, each panel should be about 34.5 inches wide for standard fullness; check each panel's stated width before buying.
Rod 70 inches, total panel width 105 inches, and 60 inch panels for floor length, 52 inches for apron length, or 48 inches for sill length.
Floor length in this calculator is measured to the floor from the rod. Some people prefer a slight break or puddle, which adds an inch or more; if you want puddling, add that to the floor length rather than using the chart figure as-is.